London: Scotland Yard has started using lie detector tests on terror informants to ensure the quality of the intelligence is strong, according to a media report.

The Metropolitan Police’s counter-terrorism command have launched a top-secret scheme to get their sources undertake polygraph examinations in an attempt to weed out lies and misinformation, The Sunday Times reports.

Representational image Reuters

The programme, which is believed to be unprecedented in British policing, is an attempt to verify intelligence from people who are often of questionable integrity as they themselves operate in the criminal underworld.

"We are not prepared to discuss this," Scotland Yard said in reference to the scheme.

News of the scheme, overseen by Mark Rowley, Britain’s most senior counter-terrorism officer, has emerged in the wake of four terrorist attacks in the UK in four months that killed 36 people.

Some blamed the attacks on a failure of intelligence, although MI5 and the police say they are overstretched and grappling with a heightened terror threat after the emergence of Islamic State in Iraq and Syria.

British Pakistani Khuram Butt, who led the London Bridge attack last month, was once placed under 24-hour surveillance by police before a decision was taken to deploy finite resources elsewhere.

British prime minister Theresa May has asked UK security services to review their protocols after it also emerged MI5 had been warned that the Manchester Arena suicide bomber, Salman Abedi, was dangerous.